The present invention relates to a light source unit for an exposure apparatus employed for, for example, forming a phosphor screen of a color picture tube.
Conventionally, some exposure apparatus of this type has had a structure such that a cylindrical, light-emitting tube is covered with a screen sleeve having a slit in the circumferential direction and rotated around the vertical axis normal to the axis of the tube, thereby functioning as a spotlight source. In other words, the light source unit thus obtained is arranged on the central normal line of the internal surface forming the phosphor screen of the color picture tube panel so that the slit of the screen sleeve faces the internal surface of the panel and the light from the light source is allowed to pass through a shadow mask with, for example, dotlike apertures whereby exposure patterns, corresponding to dotlike picture elements, are obtained on the photo sensitive film formed on the inner surface of the panel.
In order to prevent the adjoining picture element from being subjected to light from the light source, even when the electron beam irradiating position deviates in the radial direction directing from the center of the panel to the periphery of the panel due to the irregularity of the deflection coil fitting position or the like, it is desirable that the exposure pattern be flat and small especially in the above-mentioned radial direction of the panel, because the space between the adjoining exposure patterns thus becomes large in the radial direction, enabling a sufficient allowance to be obtained for the scattering of the electron beams in the beam direction.
However, the problem arises that, when the light emitting tube which may, for example, be a mercury tube, is separated from the screen sleeve and the space thus created is filled with water for cooling purposes, the degree of flatness of each exposure pattern is reduced.
Thus in the case where, for example, a light source comprising a mercury lamp 1 which is covered with a sleeve 2 and water 3 between the lamp and the sleeve as shown in FIG. 1 is self-rotated in the direction of the arrow, and an arc light 4, passing through a slit 2A, is applied to the inner surface of the panel 6 through a shadow mask 5 as shown in FIGS. 2 and 3; the position exposed in the radial or circumferential direction of the mercury lamp 1 as shown in FIG. 2, viz., the longitudinal direction of the slit 2A differs from the position exposed in the axial direction of the mercury lamp 1, viz., the cross or width direction of the slit 2A as shown in FIG. 3, so that the centers of the two spots 7 and 8 deviate from each other at the periphery of the panel 6 as shown in FIG. 4 and a synthetic exposure pattern 9 defined by a broken line is obtained.
However, since this type of apparatus is of gap type, with the mercury lamp 1 and the sleeve 2 separated as mentioned above, the exposed spot 8 in the axial direction of the mercury lamp deviates toward the periphery of the panel, making the synthetic exposure pattern 3 larger in the radial direction than when the mercury lamp 1 and the sleeve 2 are in close contact.
To prevent problems arising from the directional deviation of the exposure pattern, a method has been proposed, in the U.S. Pat. No. 4,586,799, according to which a saddle-shaped lens is employed. This method is intended to correct the apparent rise of the light source by utilizing the refraction of light through the saddle-shaped lens whose thickness is varied between the axial direction of the light-emitting tube and the direction normal to the axial direction, but the uniform correction of the apparent rise of the light source throughout the entire surface of the panel is not always satisfactory. Accordingly, since the resultant exposure pattern itself becomes a light-emitting position, it has not been possible, heretofore, to employ the rotary exposure system using a large quantity of light for the formation of a black matrix requiring a specifically high degree of accuracy in both position and shape.